1. Field of the Invention
The invention relates to press sections of a paper machine and methods for starting and operating such press sections.
2. Description of Related Technology
Paper machine press sections are known, for example, from EP 107,606. According to FIG. 1 of EP 107,606, press roll pairs are provided, each of which forms a press gap or nip. A continuous felt belt that takes up water from the web, which is known as a "dewatering felt," travels through each press gap. Additionally, an impervious, continuous loop pressing belt travels through both press gaps in succession and through some guide rolls. The web to be dewatered comes into contact with the belt in the first press gap and then it is guided by the belt to the second press gap. In this configuration, directly behind each of the two press gaps (i.e. directly downstream of the press gaps with respect to a direction of travel of the web), the dewatering felt cooperating with the press gap separates from the web to be dewatered and thus the transport of the web occurs entirely without the involvement of the dewatering felt. As a result of this, remoistening of the web from the dewatering felts is avoided. In this way, an attempt is made to increase the dewatering capacity of the press part, i,e., to have the web at a higher dry content when it leaves the press part. The disadvantages of such a configuration and other known press parts is that upon starting the press part, blockages and the related operational disturbances sometimes occur, or the course of the paper web is not unequivocally defined, causing disturbances in the operation of the press section.
Furthermore, in spite of the fact that many press section embodiments are known in the art, there is still a demand to increase the performance of known press sections, especially with respect to web dry content, optimum web guidance, symmetrical dewatering, and especially uniformity of the properties of the two sides of the paper web.